Mirror unit and optical module

ABSTRACT

A mirror unit  2  includes a mirror device  20  including a base  21  and a movable mirror  22 , an optical function member  13 , and a fixed mirror  16  that is disposed on a side opposite to the mirror device  20  with respect to the optical function member  13 . The optical function member  13  is provided with a light transmitting portion  14  that constitutes a part of an optical path between the beam splitter unit  3  and the fixed mirror  16 . The light transmitting portion  14  is a portion that corrects an optical path difference that occurs between an optical path between the beam splitter unit  3  and the movable mirror  22  and the optical path between the beam splitter unit  3  and the fixed mirror  16 . The second surface  21   b  of the base  21  and the third surface  13   a  of the optical function member  13  are joined to each other.

TECHNICAL FIELD

The present disclosure relates to a mirror unit and an optical module.

BACKGROUND ART

As a micro electro mechanical systems (MEMS) device that is constituted by a silicon on insulator (SOI) substrate, a mirror device including a base, and a movable mirror that is supported in the base to be movable along a thickness direction of the base is known (for example, refer to Patent Literature 1).

CITATION LIST Patent Literature

Patent Literature 1: US Unexamined Patent Publication No. 2008/0284078

SUMMARY OF INVENTION Technical Problem

The above-described mirror device can provide high-accuracy Fourier transformation type infrared spectral analyzer (FTIR), and thus the mirror device has attracted attention.

An object of the present disclosure is to provide a mirror unit that is suitable to constitute a high-accuracy interference optical system, and an optical module including the mirror unit.

Solution to Problem

According to an aspect of the present disclosure, there is provided a mirror unit including: a mirror device that includes a base including a first surface and a second surface opposite to the first surface, and a movable mirror supported in the base to be movable along a first direction that intersects the first surface; an optical function member including a third surface that faces the second surface, and a fourth surface opposite to the third surface; and a fixed mirror that is disposed on a side opposite to the mirror device with respect to the optical function member. The optical function member is provided with a light transmitting portion that constitutes a part of an optical path between a beam splitter unit that constitutes an interference optical system in combination with the movable mirror and the fixed mirror, and the fixed mirror. The light transmitting portion is a portion that corrects an optical path difference that occurs between an optical path between the beam splitter unit and the movable mirror, and the optical path between the beam splitter unit and the fixed mirror. The second surface of the base and the third surface of the optical function member are joined to each other.

In the mirror unit, the optical function member is disposed between the mirror device and the fixed mirror, and the base of the mirror device is joined to the optical function member. Accordingly, the base is stably held in a state in which deformation of the base is suppressed. Accordingly, it is possible to operate the movable mirror in the mirror device with accuracy. In addition, the optical function member is provided with the light transmitting portion that constitutes a part of the optical path between the beam splitter unit and the fixed mirror, and the light transmitting portion is a portion that corrects an optical path difference that occurs between the optical path between the beam splitter unit and the movable mirror, and the optical path between the beam splitter unit and the fixed mirror. Accordingly, it is possible to correct an optical path difference between the both optical paths so that a difference between an optical path length of the optical path between the beam splitter unit and the movable mirror (optical path length in consideration of a refractive index of each medium through which the optical path passes), and an optical path length of the optical path between the beam splitter unit and the fixed mirror decreases. As described above, according to the mirror unit, it is possible to constitute a high-accuracy interference optical system.

In the mirror unit according to the aspect of the present disclosure, the second surface of the base and the third surface of the optical function member may be joined to each other by direct bonding. According to this, it is possible to realize strong joining between the base of the mirror device and the optical function member.

In the mirror unit according to the aspect of the present disclosure, the fixed mirror may be formed on the fourth surface of the optical function member. According to this, it is possible to improve position accuracy and angle accuracy of the fixed mirror with respect to the movable mirror of the mirror device.

In the mirror unit according to the aspect of the present disclosure, the optical function member may further include a fifth surface that is separated from the mirror device at least in a region where the fifth surface faces the movable mirror. According to this, for example, even when a reference position in the case of reciprocating (vibrating) the movable mirror along the first direction is aligned to the third surface of the optical function member, it is possible to reciprocate the movable mirror along the first direction while preventing the movable mirror from coming into contact with the optical function member. Alignment of the reference position in the case of reciprocating the movable mirror along the first direction to the third surface of the optical function member is particularly effective for the case of correcting an optical path difference that occurs between an optical path between the beam splitter unit and the movable mirror, and an optical path between the beam splitter unit and the fixed mirror.

In the mirror unit according to the aspect of the present disclosure, the mirror device may be constituted by a semiconductor substrate, the semiconductor substrate may include a support layer that is a first semiconductor layer, a device layer that is a second semiconductor layer, and an intermediate layer that is an insulating layer disposed between the support layer and the device layer, the second surface of the base may be a surface opposite to the intermediate layer in the device layer, and a mirror surface of the movable mirror may be provided on a surface on the intermediate layer side in the device layer. In the semiconductor substrate, the device layer is thinner than the support layer. Accordingly, for example, it is possible to make the mirror surface of the movable mirror closer to the optical function member in comparison to a “configuration in which the second surface (joining surface with the optical function member) of the base is a surface opposite to the intermediate layer in the support layer, and the mirror surface of the movable mirror is provided on a surface opposite to the intermediate layer in the device layer.” Accordingly, for example, it is possible to align the reference position in the case of reciprocating the movable mirror along the first direction to the third surface of the optical function member in an easy manner.

In the mirror unit according to the aspect of the present disclosure, the fifth surface of the optical function member may extend to an outer edge of the optical function member when viewed from the first direction. According to this, even in a case where a gas exists in a region between the movable mirror and the fifth surface of the optical function member, the gas is likely to escape from the region, and thus it is possible to suppress an operation of the movable mirror from being hindered by the gas that exists in the region.

In the mirror unit according to the aspect of the present disclosure, a surface of the light transmitting portion on the mirror device side may be located on the same plane as the third surface of the optical function member. Accordingly, for example, in the case of aligning the reference position when reciprocating the movable mirror along the first direction to the third surface of the optical function member, it is possible to correct an optical path difference between the both optical paths so that a difference between an optical path length of the optical path between the beam splitter unit and the movable mirror, and an optical path length of the optical path between the beam splitter unit and the fixed mirror decreases.

In the mirror unit according to the aspect of the present disclosure, the base may further include a sixth surface that is separated from the optical function member in a region including at least a part of an outer edge of the base when viewed from the first direction. Accordingly, when joining the second surface of the base and the third surface of the optical function member to each other, it is possible to perform handling of the mirror device by gripping the region in which the sixth surface is provided in the base.

In the mirror unit according to the aspect of the present disclosure, the outer edge of the optical function member may be located outside of the outer edge of the base when viewed from the first direction. According to this, it is possible to realize strong joining between the base of the mirror device and the optical function member. In addition, it is possible to protect the outer edge of the base.

The mirror unit according to the aspect of the present disclosure may further include a stress mitigation substrate that is attached to the fourth surface of the optical function member with the fixed mirror interposed therebetween. When the mirror unit is provided in an installation target via the stress mitigation substrate, for example, even in a case where the installation target is deformed, it is possible to suppress the deformation from having an effect on the interference optical system.

According to another aspect of the present disclosure, there is provided an optical module including: the above-described mirror unit; and a beam splitter unit that constitutes an interference optical system in combination with the movable mirror and the fixed mirror.

In the optical module, it is possible to constitute the high-accuracy interference optical system due to the above-described mirror unit.

Advantageous Effects of Invention

According to the present disclosure, it is possible to provide a mirror unit that is suitable to constitute a high-accuracy interference optical system, and an optical module including the mirror unit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an optical module of an embodiment.

FIG. 2 is a plan view of a mirror unit illustrated in FIG. 1 .

FIG. 3 is a cross-sectional view of the mirror unit which is taken along line illustrated in FIG. 2 .

FIG. 4 is a cross-sectional view of the mirror unit which is taken along line IV-IV illustrated in FIG. 2 .

FIG. 5 is a schematic cross-sectional view of a mirror device which is taken along line V-V illustrated in FIG. 2 .

FIG. 6 is a partially enlarged view of the mirror device illustrated in FIG. 2 .

FIG. 7 is a plan view of an optical function member illustrated in FIG. 2 .

FIG. 8 is a cross-sectional view of the optical module which is taken along line VIII-VIII illustrated in FIG. 1 .

FIG. 9 is a cross-sectional view of the optical module which is taken along line IX-IX illustrated in FIG. 1 .

FIG. 10 is a schematic cross-sectional view of the mirror unit and a beam splitter unit which are illustrated in FIG. 1 .

FIG. 11 is a cross-sectional view of a beam splitter unit of a modification example.

FIG. 12 is a schematic cross-sectional view of a mirror unit of the modification example.

FIG. 13 is a cross-sectional view of the mirror unit of the modification example.

FIG. 14 is a cross-sectional view of the mirror unit of the modification example.

FIG. 15 is a plan view of the mirror unit of the modification example.

FIG. 16 is a cross-sectional view for describing a process of manufacturing the mirror unit of the modification example.

FIG. 17 is a cross-sectional view for describing the process of manufacturing the mirror unit of the modification example.

FIG. 18 is a plan view of a mirror device of the modification example.

FIG. 19 is a plan view of the mirror unit of the modification example.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. The same reference numeral will be given to the same or equivalent parts in the respective drawings, and redundant description thereof will be omitted.

[Configuration of Optical Module]

As illustrated in FIG. 1 , an optical module 1 includes a mirror unit 2, a beam splitter unit 3, a light incident unit 4, a first light detector 6, a second light source 7, a second light detector 8, a support 9, a first support structure 11, and a second support structure 12. The mirror unit 2 is disposed on one side of the support 9 in a Z-axis direction (first direction), and is attached to the support 9, for example, by an adhesive. For example, the support 9 is formed of copper tungsten, and has a rectangular plate shape. The mirror unit 2 includes a movable mirror 22 that moves in the Z-axis direction, and a fixed mirror 16 of which a position is fixed (details thereof will be described later). For example, the Z-axis direction is a vertical direction, and the one side in the Z-axis direction is an upper side.

The beam splitter unit 3 is disposed on one side of the mirror unit 2 in the Z-axis direction, and is supported by the first support structure 11. The first support structure 11 is attached to the support 9, for example, by an adhesive. The light incident unit 4 is disposed on one side of the beam splitter unit 3 in an X-axis direction (a second direction that intersects the first direction), and is supported by the second support structure 12. The first light detector 6, the second light source 7, and the second light detector 8 are disposed on the one side of the beam splitter unit 3 in the Z-axis direction, and are supported by the second support structure 12. The second support structure 12 is attached to the support 9, for example, by a bolt.

In the optical module 1, an interference optical system is constituted by the beam splitter unit 3, the movable mirror 22, and the fixed mirror 16 with respect to each of measurement light L0 and laser light L10. The interference optical system which is constituted with respect to each of the measurement light L0 and the laser light L10 is, for example, a Michelson interference optical system.

With regard to the measurement light L0, interference light L1 of measurement light is detected as follows. That is, when the measurement light L0 that is incident from a first light source (not illustrated) through a measurement target (not illustrated) or the measurement light L0 that is generated from the measurement target (for example, light emitted from the measurement target itself, or the like) is incident to the beam splitter unit 3 from the light incident unit 4, the measurement light L0 is divided into a part and the remainder in the beam splitter unit 3. The part of the measurement light L0 is reflected by the movable mirror 22 that reciprocates in the Z-axis direction, and returns to the beam splitter unit 3. On the other hand, the remainder of the measurement light L0 is reflected by the fixed mirror 16 and returns to the beam splitter unit 3. The part and the remainder of the measurement light L0, which return to the beam splitter unit 3, are emitted from the beam splitter unit 3 as the interference light L1, and the interference light L1 of the measurement light is detected by the first light detector 6.

With regard to the laser light L10, interference light L11 of laser light is detected as follows. That is, when the laser light L10 emitted from the second light source 7 is incident to the beam splitter unit 3, the laser light L10 is divided into a part and the remainder in the beam splitter unit 3. The part of the laser light L10 is reflected by the movable mirror 22 that reciprocates in the Z-axis direction, and returns to the beam splitter unit 3. On the other hand, the remainder of the laser light L10 is reflected by the fixed mirror 16 and returns to the beam splitter unit 3. The part and the remainder of the laser light L10, which return to the beam splitter unit 3, are emitted from the beam splitter unit 3 as the interference light L11, and the interference light L11 of the laser light is detected by the second light detector 8.

According to the optical module 1, measurement of a position of the movable mirror 22 in the Z-axis direction can be measured based on a detection result of the interference light Lit of the laser light, and spectral analysis with respect to the measurement target can be performed based on a measurement result of the position, and a detection result of the interference light L1 of the measurement light.

[Configuration of Mirror Unit]

As illustrated in FIG. 2 , FIG. 3 , and FIG. 4 , the mirror unit 2 includes a mirror device 20, an optical function member 13, the fixed mirror 16, and a stress mitigation substrate 17. The mirror device 20 includes a base 21, the movable mirror 22, and a drive unit 23.

The base 21 includes a first surface 21 a (surface on the one side in the Z-axis direction) and a second surface 21 b opposite to the first surface 21 a. Each of the first surface 21 a and the second surface 21 b is a main surface of the base 21. For example, the base 21 has a rectangular plate shape, and a size of approximately 10 mm×15 mm×0.35 mm (thickness). The movable mirror 22 includes a mirror surface 22 a, and a movable unit 22 b in which the mirror surface 22 a is disposed. The movable mirror 22 is supported in the base 21 so that the movable mirror 22 can move in the Z-axis direction perpendicular to the first surface 21 a (a first direction that intersects a first surface). The drive unit 23 moves the movable mirror 22 in the Z-axis direction.

A pair of light passage portions 24 and 25 are provided in the mirror device 20. The pair of light passage portions 24 and 25 are respectively disposed on both sides of the movable mirror 22 in the X-axis direction. The light passage portion 24 constitutes a first portion of an optical path between the beam splitter unit 3 and the fixed mirror 16. In this embodiment, the light passage portion 25 does not function as a light passage portion.

Here, a configuration of the mirror device 20 will be described in detail with reference to FIG. 2 , FIG. 5 , and FIG. 6 . FIG. 5 is a schematic cross-sectional view of the mirror device 20 illustrated in FIG. 3 , and FIG. 5 schematically illustrates the mirror device 20, for example, in a state in which dimensions in the Z-axis direction are enlarged in comparison to actual dimensions.

The base 21, the movable unit 22 b of the movable mirror 22, and the drive unit 23 are constituted by a silicon on insulator (SOI) substrate (semiconductor substrate) 100. That is, the mirror device 20 is constituted by the SOI substrate 100. For example, the mirror device 20 is formed in a rectangular plate shape. The SOI substrate 100 includes a support layer 101, a device layer 102, and an intermediate layer 103. The support layer 101 is a first silicon layer (a first semiconductor layer). The device layer 102 is a second silicon layer (a second semiconductor layer). The intermediate layer 103 is an insulating layer that is disposed between the support layer 101 and the device layer 102. The SOI substrate 100 includes the support layer 101, the intermediate layer 103, and the device layer 102 in this order from the one side in the Z-axis direction.

The base 21 is constituted by a part of the support layer 101, the device layer 102, and the intermediate layer 103. The first surface 21 a of the base 21 is a surface of the support layer 101 which is opposite to the intermediate layer 103. The second surface 21 b of the base 21 is a surface of the device layer 102 which is opposite to the intermediate layer 103. The support layer 101 that constitutes the base 21 is thicker than the device layer 102 that constitutes the base 21. For example, the thickness of the support layer 101 that constitutes the base 21 is approximately four times the thickness of the device layer 102 that constitutes the base 21. As will be described later, in the mirror unit 2, the second surface 21 b of the base 21 and a third surface 13 a of the optical function member 13 are jointed to each other (refer to FIG. 3 and FIG. 4 ).

The movable mirror 22 is disposed in a state in which an intersection between an axial line R1 and an axial line R2 is set as the central position (gravity center position). The axial line R1 is a straight line that extends in the X-axis direction. The axial line R2 is a straight line that extends in a Y-axis direction. When viewed from the Z-axis direction, in the mirror device 20, a portion other than a portion that overlaps a sixth surface 21 d of the base 21 to be described later has a shape that is linearly symmetric to each of the axial line R1 and the axial line R2.

The movable mirror 22 (movable unit 22 b) includes an arrangement portion 221, a frame portion 222, a pair of connection portions 223, and a rib portion 224. The arrangement portion 221, the frame portion 222, and the pair of connection portions 223 are constituted by a part of the device layer 102. The arrangement portion 221 has a circular shape when viewed from the Z-axis direction. The arrangement portion 221 includes a central portion 221 a and an edge portion 221 b. For example, the mirror surface 22 a is provided on a surface 221 as of the central portion 221 a on the one side in the Z-axis direction by forming a metal film (metal layer) thereon. The mirror surface 22 a extends perpendicular to the Z-axis direction, and has a circular shape. The surface 221 as of the central portion 221 a is a surface on the intermediate layer 103 side in the device layer 102. The mirror surface 22 a is located on the other side in the Z-axis direction in comparison to the first surface 21 a of the base 21. In other words, the first surface 21 a is located on the one side in the Z-axis direction in comparison to the mirror surface 22 a. The edge portion 221 b surrounds the central portion 221 a when viewed from the Z-axis direction.

The frame portion 222 extends in an annular shape to surround the arrangement portion 221 with a predetermined gap from the arrangement portion 221 when viewed from the Z-axis direction. For example, the frame portion 222 has a circular ring shape when viewed from the Z-axis direction. Each of the pair of connection portions 223 connects the arrangement portion 221 and the frame portion 222 to each other. The pair of connection portions 223 are respectively disposed on both sides of the arrangement portion 221 in the Y-axis direction.

The rib portion 224 is constituted by the support layer 101 and the intermediate layer 103 which are disposed on the device layer 102. The rib portion 224 includes an inner rib portion 224 a, an outer rib portion 224 b, and a pair of connection rib portions 224 c. The inner rib portion 224 a is disposed on a surface of the edge portion 221 b on the one side in the Z-axis direction. The inner rib portion 224 a surrounds the mirror surface 22 a when viewed from the Z-axis direction. For example, an outer edge of the inner rib portion 224 a extends along an outer edge of the arrangement portion 221 with a predetermined gap from the outer edge of the arrangement portion 221 when viewed from the Z-axis direction. An inner edge of the inner rib portion 224 a extends along an outer edge of the mirror surface 22 a with a predetermined gap from the outer edge of the mirror surface 22 a when viewed from the Z-axis direction. An end surface 224 as of the inner rib portion 224 a on the one side in the Z-axis direction is located on the one side in the Z-axis direction in comparison to the mirror surface 22 a.

The outer rib portion 224 b is disposed on a surface of the frame portion 222 on the one side in the Z-axis direction. The outer rib portion 224 b surrounds the inner rib portion 224 a and the mirror surface 22 a when viewed from the Z-axis direction. For example, an outer edge of the outer rib portion 224 b extends along an outer edge of the frame portion 222 with a predetermined gap from the outer edge of the frame portion 222 when viewed from the Z-axis direction. An inner edge of the outer rib portion 224 b extends along an inner edge of the frame portion 222 with a predetermined gap from the inner edge of the frame portion 222 when viewed from the Z-axis direction. An end surface 224 bs of the outer rib portion 224 b on the one side in the Z-axis direction is located on the one side in the Z-axis direction in comparison to the mirror surface 22 a.

The pair of connection rib portions 224 c are respectively disposed on surfaces of the pair of connection portions 223 on the one side in the Z-axis direction. The connection rib portions 224 c connect the inner rib portion 224 a and the outer rib portion 224 b to each other. End surfaces 224 cs of the connection rib portions 224 c on the one side in the Z-axis direction are located on the one side in the Z-axis direction in comparison to the mirror surface 22 a.

The thickness of the inner rib portion 224 a, the thickness of the outer rib portion 224 b, and the thickness of the respective connection rib portions 224 c in the Z-axis direction are the same as each other. That is, the thickness of the support layer 101 that constitutes the inner rib portion 224 a, the outer rib portion 224 b, and the respective connection rib portions 224 e is the same in each case. The end surface 224 as of the inner rib portion 224 a, the end surface 224 bs of the outer rib portion 224 b, and the end surfaces 224 cs of the respective connection rib portions 224 c are located on the same plane perpendicular to the Z-axis direction. The support layer 101 that constitutes the inner rib portion 224 a, the outer rib portion 224 b, and the respective connection rib portions 224 c is thinner than the support layer 101 that constitutes the base 21. Accordingly, the end surfaces 224 as, 224 bs, and 224 cs are located on the one side in the Z-axis direction in comparison to the first surface 21 a of the base 21. In other words, the first surface 21 a is located on the other side in the Z-axis direction in comparison to the end surfaces 224 as, 224 bs, and 224 cs.

When viewed from the Z-axis direction, a width of the outer rib portion 224 b is wider than a width of the inner rib portion 224 a. The width of the inner rib portion 224 a when viewed from the Z-axis direction is a length of the inner rib portion 224 a in a direction perpendicular to the extending direction of the inner rib portion 224 a, and is a length of the inner rib portion 224 a in a radial direction of the inner rib portion 224 a in this embodiment. This is also true of a width of the outer rib portion 224 b when viewed from the Z-axis direction. A width of each of the connection rib portions 224 c is wider than the width of each of the inner rib portion 224 a and the outer rib portion 224 b. The width of each of the connection rib portion 224 c is a length of each of the connection rib portion 224 c along the extending direction of the inner rib portion 224 a.

The drive unit 23 includes a first elastic support unit 26, a second elastic support unit 27, and an actuator unit 28. The first elastic support unit 26, the second elastic support unit 27, and the actuator unit 28 are constituted by a part of the device layer 102.

Each of the first elastic support unit 26 and the second elastic support unit 27 is connected between the base 21 and the movable mirror 22. The first elastic support unit 26 and the second elastic support unit 27 support the movable mirror 22 so that the movable mirror 22 (movable unit 22 b) can move in the Z-axis direction.

The first elastic support unit 26 includes a pair of levers 261, a first link member 262, a second link member 263, a pair of beam members 264, an intermediate member 265, a pair of first torsion bars (first torsion support portions) 266, a pair of second torsion bars (second torsion support portions) 267, a pair of non-linearity mitigation springs 268, and a plurality of electrode support portions 269.

The pair of levers 261 are respectively disposed on both sides of the light passage portion 24 in the Y-axis direction, and face each other in the Y-axis direction. Each of the levers 261 has a plate shape that extends along a plane perpendicular to the Z-axis direction. The lever 261 includes a first portion 261 a, a second portion 261 b that is disposed on a side opposite to the movable mirror 22 with respect to the first portion 261 a, and a third portion 261 c that is connected to the first portion 261 a and the second portion 261 b. The first portion 261 a and the second portion 261 b extend in the X-axis direction. A length of the first portion 261 a in the X-axis direction is shorter than a length of the second portion 261 b in the X-axis direction. The third portions 261 c of the pair of levers 261 obliquely extend to be spaced away from each other as going away from the movable mirror 22.

The first link member 262 bridges first ends 261 d of the pair of levers 261 on a side opposite to the movable mirror 22. The first link member 262 has a plate shape that extends along a plane perpendicular to the Z-axis direction, and extends in the Y-axis direction. The second link member 263 bridges second ends 261 e of the pair of levers 261 on the movable mirror 22 side. The second link member 263 has a plate shape that extends along a plane perpendicular to the Z-axis direction, and extends in the Y-axis direction. A width of the second link member 263 in the X-axis direction is narrower than a width of the first link member 262 in the X-axis direction. A length of the second link member 263 in the Y-axis direction is shorter than a length of the first link member 262 in the Y-axis direction.

The pair of beam members 264 respectively bridge the second portions 261 b of the pair of levers 261 and the first link member 262. The respective beam members 264 have a plate shape that extends along a plane perpendicular to the Z-axis direction. The pair of beam members 264 obliquely extend to approach each other as going away from the movable mirror 22. The pair of levers 261, the first link member 262, the second link member 263, and the pair of beam members 264 define the light passage portion 24. The light passage portion 24 has a polygonal shape when viewed from the Z-axis direction. For example, the light passage portion 24 is a cavity (hole). Alternatively, a material having optical transparency with respect to the measurement light L0 and the laser light L10 may be disposed in the light passage portion 24.

The intermediate member 265 has a plate shape that extends along a plane perpendicular to the Z-axis direction, and extends in the Y-axis direction. The intermediate member 265 is disposed between the movable mirror 22 and the second link member 263 (in other words, between the movable mirror 22 and the light passage portion 24). The intermediate member 265 is connected to the movable mirror 22 through the non-linearity mitigation springs 268 as to be described later.

The pair of first torsion bars 266 respectively bridge the first end 261 d of one lever 261 and the base 21, and the first end 261 d of the other lever 261 and the base 21. That is, the pair of first torsion bars 266 are respectively connected between the pair of levers 261 and the base 21. The first torsion bars 266 extend in the Y-axis direction. The pair of first torsion bars 266 are disposed on the same central line parallel to the Y-axis direction. In this embodiment, the central line of the first torsion bars 266 and the central line of the first link member 262 are located on the same straight line. A protrusion 261 f that protrudes outward in the Y-axis direction is provided in each of the first ends 261 d of the levers 261, and each of the first torsion bars 266 is connected to the protrusion 261 f.

The pair of second torsion bars 267 respectively bridge the second end 261 e of one lever 261 and one end of the intermediate member 265, and the second end 261 e of the other lever 261 and the other end of the intermediate member 265. That is, the pair of second torsion bars 267 are respectively connected between the pair of levers 261 and the movable mirror 22. The respective second torsion bars 267 extend in the Y-axis direction. The pair of second torsion bars 267 are disposed on the same central line parallel to the Y-axis direction.

The pair of non-linearity mitigation springs 268 are connected between the movable mirror 22 and the intermediate member 265. That is, the pair of non-linearity mitigation springs 268 are connected between the movable mirror 22 and the second torsion bar 267. Each of the non-linearity mitigation springs 268 includes a meandering portion 268 a that extends in a meandering manner when viewed from the Z-axis direction. The meandering portion 268 a includes a plurality of straight portions 268 b which extend in the Y-axis direction and are aligned in the X-axis direction, and a plurality of folded portions 268 c which alternately connect both ends of the plurality of straight portions 268 b. One end of the meandering portion 268 a is connected to the intermediate member 265, and the other end of the meandering portion 268 a is connected to the frame portion 222. In the meandering portion 268 a, a portion on the frame portion 222 side has a shape along the outer edge of the frame portion 222.

The non-linearity mitigation spring 268 is constituted as follows. In a state in which the movable mirror 22 has moved in the Z-axis direction, the amount of deformation of the non-linearity mitigation spring 268 around the Y-axis direction becomes smaller than the amount of deformation of each of the first torsion bar 266 and the second torsion bar 267 around the Y-axis direction, and the amount of deformation of the non-linearity mitigation spring 268 in the X-axis direction becomes larger than the amount of deformation of each of the first torsion bar 266 and the second torsion bar 267 in the X-axis direction. Accordingly, it is possible to suppress occurrence of non-linearity in twist deformation of the first torsion bar 266 and the second torsion bar 267, and it is possible to suppress deterioration of control characteristics of the movable mirror 22 due to the non-linearity. The amount of deformation of the first torsion bar 266, the second torsion bar 267, and the non-linearity mitigation spring 268 around the Y-axis direction represents, for example, an absolute value of a twist amount (twist angle). The amount of deformation of the first torsion bar 266, the second torsion bar 267, and the non-linearity mitigation spring 268 in the X-axis direction represents, for example, an absolute value of a deflection amount. The amount of deformation of a member around the Y-axis direction represents the amount of deformation of the member in a peripheral direction of a circle of which the center is set to an axial line that passes through the center of the member and is parallel to the Y-axis. This is also true of first torsion bars 276, second torsion bars 277, and a non-linearity mitigation spring 278 to be described later.

The plurality of electrode support portions 269 include a pair of first electrode support portions 269 a, a pair of second electrode support portions 269 b, and a pair of third electrode support portions 269 c. Each of the electrode support portions 269 a, 269 b, and 269 c has a plate shape that extends along a plane perpendicular to the Z-axis direction, and extends in the Y-axis direction. Each of the electrode support portions 269 a, 269 b, and 269 c extends from the second portion 261 b of the lever 261 toward a side opposite to the light passage portion 24. The pair of first electrode support portions 269 a are disposed on the same central line parallel to the Y-axis direction. The pair of second electrode support portions 269 b are disposed on the same central line parallel to the Y-axis direction. The pair of third electrode support portions 269 c are disposed on the same central line parallel to the Y-axis direction. In the X-axis direction, the first electrode support portions 269 a, the second electrode support portions 269 b, and the third electrode support portions 269 c are aligned in this order from the movable mirror 22 side.

The second elastic support unit 27 includes a pair of levers 271, a first link member 272, a second link member 273, a pair of beam members 274, an intermediate member 275, a pair of first torsion bars (first torsion support portions) 276, a pair of second torsion bars (second torsion support portions) 277, a pair of non-linearity mitigation springs 278, and a plurality of electrode support portions 279.

The pair of levers 271 are respectively disposed on both sides of the light passage portion 25 in the Y-axis direction, and face each other in the Y-axis direction. Each of the levers 271 has a plate shape that extends along a plane perpendicular to the Z-axis direction. The lever 271 includes a first portion 271 a, a second portion 271 b that is disposed on a side opposite to the movable mirror 22 with respect to the first portion 271 a, and a third portion 271 c that is connected to the first portion 271 a and the second portion 271 b. The first portion 271 a and the second portion 271 b extend in the X-axis direction. A length of the first portion 271 a in the X-axis direction is shorter than a length of the second portion 271 b in the X-axis direction. The third portions 271 c of the pair of levers 271 obliquely extend to be spaced away from each other as going away from the movable mirror 22.

The first link member 272 bridges first ends 271 d of the pair of levers 271 on a side opposite to the movable mirror 22. The first link member 272 has a plate shape that extends along a plane perpendicular to the Z-axis direction, and extends in the Y-axis direction. The second link member 273 bridges second ends 271 e of the pair of levers 271 on the movable mirror 22 side. The second link member 273 has a plate shape that extends along a plane perpendicular to the Z-axis direction, and extends in the Y-axis direction. A width of the second link member 273 in the X-axis direction is narrower than a width of the first link member 272 in the X-axis direction. A length of the second link member 273 in the Y-axis direction is shorter than a length of the first link member 272 in the Y-axis direction.

The pair of beam members 274 respectively bridge the second portions 271 b of the pair of levers 271 and the first link member 272. The respective beam members 274 have a plate shape that extends along a plane perpendicular to the Z-axis direction. The pair of beam members 274 obliquely extend to approach each other as going away from the movable mirror 22. The pair of levers 271, the first link member 272, the second link member 273, and the pair of beam members 274 define the light passage portion 25. The light passage portion 25 has a polygonal shape when viewed from the Z-axis direction. For example, the light passage portion 25 is a cavity (hole). Alternatively, a material having optical transparency with respect to the measurement light L0 and the laser light L10 may be disposed in the light passage portion 25.

The intermediate member 275 has a plate shape that extends along a plane perpendicular to the Z-axis direction, and extends in the Y-axis direction. The intermediate member 275 is disposed between the movable mirror 22 and the second link member 273 (in other words, between the movable mirror 22 and the light passage portion 25). The intermediate member 275 is connected to the movable mirror 22 through the non-linearity mitigation springs 278 as to be described later.

The pair of first torsion bars 276 respectively bridge the first end 271 d of one lever 271 and the base 21, and the first end 271 d of the other lever 271 and the base 21. That is, the pair of first torsion bars 276 are respectively connected between the pair of levers 271 and the base 21. The first torsion bars 276 extend in the Y-axis direction. The pair of first torsion bars 276 are disposed on the same central line parallel to the Y-axis direction. In this embodiment, the central line of the first torsion bars 276 and the central line of the first link member 272 are located on the same straight line. A protrusion 271 f that protrudes outward in the Y-axis direction is provided in each of the first ends 271 d of the levers 271, and each of the first torsion bars 276 is connected to the protrusion 271 f.

The pair of second torsion bars 277 respectively bridge the second end 271 e of one lever 271 and one end of the intermediate member 275, and the second end 271 e of the other lever 271 and the other end of the intermediate member 275. That is, the pair of second torsion bars 277 are respectively connected between the pair of levers 271 and the movable mirror 22. The respective second torsion bars 277 extend in the Y-axis direction. The pair of second torsion bars 277 are disposed on the same central line parallel to the Y-axis direction.

The pair of non-linearity mitigation springs 278 are connected between the movable mirror 22 and the intermediate member 275. That is, the pair of non-linearity mitigation springs 278 are connected between the movable mirror 22 and the second torsion bar 277. Each of the non-linearity mitigation springs 278 includes a meandering portion 278 a that extends in a meandering manner when viewed from the Z-axis direction. The meandering portion 278 a includes a plurality of straight portions 278 b which extend in the Y-axis direction and are aligned in the X-axis direction, and a plurality of folded portions 278 c which alternately connect both ends of the plurality of straight portions 278 b. One end of the meandering portion 278 a is connected to the intermediate member 275, and the other end of the meandering portion 278 a is connected to the frame portion 222. In the meandering portion 278 a, a portion on the frame portion 222 side has a shape along the outer edge of the frame portion 222.

The non-linearity mitigation spring 278 is constituted as follows. In a state in which the movable mirror 22 has moved in the Z-axis direction, the amount of deformation of the non-linearity mitigation spring 278 around the Y-axis direction becomes smaller than the amount of deformation of each of the first torsion bar 276 and the second torsion bar 277 around the Y-axis direction, and the amount of deformation of the non-linearity mitigation spring 278 in the X-axis direction becomes larger than the amount of deformation of each of the first torsion bar 276 and the second torsion bar 277 in the X-axis direction. Accordingly, it is possible to suppress occurrence of non-linearity in twist deformation of the first torsion bar 276 and the second torsion bar 277, and it is possible to suppress deterioration of control characteristics of the movable mirror 22 due to the non-linearity.

The plurality of electrode support portions 279 includes a pair of first electrode support portions 279 a, a pair of second electrode support portions 279 b, and a pair of third electrode support portions 279 c. Each of the electrode support portions 279 a, 279 b, and 279 c has a plate shape that extends along a plane perpendicular to the Z-axis direction, and extends in the Y-axis direction. Each of the electrode support portions 279 a, 279 b, and 279 c extends from the second portion 271 b of the lever 271 toward a side opposite to the light passage portion 25. The pair of first electrode support portions 279 a are disposed on the same central line parallel to the Y-axis direction. The pair of second electrode support portions 279 b are disposed on the same central line parallel to the Y-axis direction. The pair of third electrode support portions 279 c are disposed on the same central line parallel to the Y-axis direction. In the X-axis direction, the first electrode support portions 279 a, the second electrode support portions 279 b, and the third electrode support portions 279 c are aligned in this order from the movable mirror 22 side.

The actuator unit 28 moves the movable mirror 22 in the Z-axis direction. The actuator unit 28 includes a fixed comb electrode 281, a movable comb electrode 282, a fixed comb electrode 283, and a movable comb electrode 284. Positions of the fixed comb electrodes 281 and 283 are fixed. The movable comb electrodes 282 and 284 move in accordance with movement of the movable mirror 22.

The fixed comb electrode 281 is provided on a part of a surface, which faces the electrode support portions 269, of the device layer 102 of the base 21. The fixed comb electrode 281 includes a plurality of fixed comb fingers 281 a which extend along a plane perpendicular to the Y-axis direction. The fixed comb fingers 281 a are aligned in the Y-axis direction with a predetermined gap therebetween.

The movable comb electrode 282 is provided on a surface of each of the first electrode support portions 269 a on the movable mirror 22 side, on surfaces of each of the second electrode support portions 269 b on both sides in the X-axis direction, and on a surface of each of the third electrode support portion 269 c on the movable mirror 22 side. The movable comb electrode 282 includes a plurality of movable comb fingers 282 a which extend along a plane perpendicular to the Y-axis direction. The movable comb fingers 282 a are aligned in the Y-axis direction with a predetermined gap therebetween.

In the fixed comb electrode 281 and the movable comb electrode 282, the plurality of fixed comb fingers 281 a and the plurality of movable comb fingers 282 a are alternately arranged. That is, each of the fixed comb fingers 281 a of the fixed comb electrode 281 is located between the movable comb fingers 282 a of the movable comb electrode 282. The fixed comb fingers 281 a and the movable comb fingers 282 a, which are adjacent to each other, face each other in the Y-axis direction. A distance between the fixed comb finger 281 a and the movable comb finger 282 a, which are adjacent to each other, is approximately several μm.

The fixed comb electrode 283 is provided on a part of a surface, which faces the electrode support portions 279, of the device layer 102 of the base 21. The fixed comb electrode 283 includes a plurality of fixed comb fingers 283 a which extend along a plane perpendicular to the Y-axis direction. The fixed comb fingers 283 a are aligned in the Y-axis direction with a predetermined gap therebetween.

The movable comb electrode 284 is provided on a surface of each of the first electrode support portion 279 a on the movable mirror 22 side, on surfaces of each of the second electrode support portions 279 b on both sides in the X-axis direction, and on a surface of each of the third electrode support portion 279 c on the movable mirror 22 side. The movable comb electrode 284 includes a plurality of movable comb fingers 284 a which extend along a plane perpendicular to the Y-axis direction. The movable comb fingers 284 a are aligned in the Y-axis direction with a predetermined gap therebetween.

In the fixed comb electrode 283 and the movable comb electrode 284, the plurality of fixed comb fingers 283 a and the plurality of movable comb fingers 284 a are alternately arranged. That is, each of the fixed comb fingers 283 a of the fixed comb electrode 283 is located between the movable comb fingers 284 a of the movable comb electrode 284. The fixed comb fingers 283 a and the movable comb fingers 284 a, which are adjacent to each other, face each other in the Y-axis direction. For example, a distance between the fixed comb finger 283 a and the movable comb finger 284 a, which are adjacent to each other, is approximately several μm.

A plurality of electrode pads 211 are provided in the base 21. The electrode pads 211 are disposed on a surface of the device layer 102 in an opening 213 formed in the first surface 21 a of the base 21 to reach the device layer 102. Some of the plurality of electrode pads 211 are electrically connected to the fixed comb electrode 281 or the fixed comb electrode 283 via the device layer 102. Several other electrode pads 211 among the plurality of electrode pads 211 are electrically connected to the movable comb electrode 282 or the movable comb electrode 284 via the first elastic support unit 26 or the second elastic support unit 27. In addition, a pair of electrode pads 212 which can be used as ground electrodes are provided in the base 21. The pair of electrode pads 212 are disposed on the first surface 21 a to be located on both sides of the movable mirror 22 in the Y-axis direction.

In the mirror device 20 configured as described above, an electric signal for moving the movable mirror 22 in the Z-axis direction, is input to the drive unit 23 through a lead pin 113 to be described later and a wire (not illustrated). Accordingly, for example, an electrostatic force is generated between the fixed comb electrode 281 and the movable comb electrode 282 which face each other, and the fixed comb electrode 283 and the movable comb electrode 284 which face each other so that the movable mirror 22 moves to one side in the Z-axis direction. At this time, the first torsion bars 266 and 276 and the second torsion bars 267 and 277 in the first elastic support unit 26 and the second elastic support unit 27 are twisted, and an elastic force is generated in the first elastic support unit 26 and the second elastic support unit 27. In the mirror device 20, when a periodic electric signal is applied to the drive unit 23, it is possible to reciprocate the movable mirror 22 in the Z-axis direction at a resonance frequency level. In this manner, the drive unit 23 functions as an electrostatic actuator.

As illustrated in FIG. 2 , FIG. 3 , FIG. 4 , and FIG. 7 , the optical function member 13 includes the third surface 13 a (a surface on the one side in the Z-axis direction) that faces the second surface 21 b of the base 21, and a fourth surface 13 b opposite to the third surface 13 a. When viewed from the Z-axis direction, an outer edge 13 c of the optical function member 13 is located outside of an outer edge 21 c of the base 21. That is, when viewed from the Z-axis direction, the outer edge 13 c of the optical function member 13 surrounds the outer edge 21 c of the base 21. The optical function member 13 is integrally formed by a material having transparency with respect to the measurement light L0 and the laser light L10. For example, the optical function member 13 is formed in a rectangular plate shape by glass, and has a size of approximately 15 mm×20 mm×4 mm (thickness). For example, the material of the optical function member 13 is selected in accordance with a sensitivity wavelength of the optical module 1. For example, the material is set to glass in a case where the sensitivity wavelength of the optical module 1 is a near infrared region, and the material is set to silicon in a case where the sensitivity wavelength of the optical module 1 is an intermediate infrared region.

A pair of light transmitting portions 14 and 15 are provided in the optical function member 13. The light transmitting portion 14 is a portion, which faces the light passage portion 24 of the mirror device 20 in the Z-axis direction, in the optical function member 13. The light transmitting portion 15 is a portion, which faces the light passage portion 25 of the mirror device 20 in the Z-axis direction, in the optical function member 13. A surface 14 a of the light transmitting portion 14 on the mirror device 20 side, and a surface 15 a of the light transmitting portion 15 on the mirror device 20 side are located on the same plane as the third surface 13 a. The light transmitting portion 14 constitutes a second portion (partial portion) of an optical path between the beam splitter unit 3 and the fixed mirror 16. The light transmitting portion 14 is a portion that corrects an optical path difference that occurs between an optical path between the beam splitter unit 3 and the movable mirror 22, and an optical path between the beam splitter unit 3 and the fixed mirror 16. In this embodiment, the light transmitting portion 15 does not function as a light transmitting portion.

The optical function member 13 includes a fifth surface 13 d that faces the movable mirror 22 and the drive unit 23 of the mirror device 20. The fifth surface 13 d is located on the fourth surface 13 b side in comparison to the third surface 13 a. The fifth surface 13 d extends to the outer edge 13 c of the optical function member 13 when viewed from the Z-axis direction. In this embodiment, the fifth surface 13 d extends to a pair of opposite sides which extend in the Y-axis direction (a direction that intersects the first direction and the second direction) in the outer edge 13 c of the optical function member 13 while surrounding ends of the respective light transmitting portions 14 and 15 on the mirror device 20 side.

The third surface 13 a of the optical function member 13 is joined to the second surface 21 b of the base 21 by direct bonding (for example, plasma activation bonding, surface-activated room-temperature bonding (SAB), atomic diffusion bonding (ADB), anodic bonding, fusion bonding, hydrophilic bonding, and the like). In this embodiment, the third surface 13 a extends to face a plurality of the electrode pads 211 and 212 provided in the base 21 on both sides of the fifth surface 13 d in the Y-axis direction. Here, the fifth surface 13 d is located on the fourth surface 13 b side in comparison to the third surface 13 a, and thus the fifth surface 13 d is separated from the mirror device 20 in a region where the fifth surface 13 d faces the movable mirror 22 and the drive unit 23. In addition, the surface 14 a of the light transmitting portion 14 and the surface 15 a of the light transmitting portion 15 respectively face the light passage portions 24 and 25 of the mirror device 20. Accordingly, in the mirror unit 2, when the movable mirror 22 reciprocates in the Z-axis direction, the movable mirror 22 and the drive unit 23 are prevented from coming into contact with the optical function member 13.

A sixth surface 21 d, which is separated from the optical function member 13 in a state in which the third surface 13 a of the optical function member 13 and the second surface 21 b of the base 21 are joined to each other, is provided in the base 21 of the mirror device 20. The sixth surface 21 d is separated from the optical function member 13 in a region that includes at least a part of an outer edge of the base 21 when viewed from the Z-axis direction. In this embodiment, the sixth surface 21 d is formed by removing the device layer 102 and the intermediate layer 103 along one side, which extends in the Y-axis direction, in the outer edge of the base 21 by etching. In addition, a plurality of reference holes 13 e are formed in the third surface 13 a of the optical function member 13. In this embodiment, the plurality of reference holes 13 e are formed in the third surface 13 a to correspond to a plurality of corners of the base 21. When the third surface 13 a of the optical function member 13 and the second surface 21 b of the base 21 are joined to each other, handling of the mirror device 20 is performed in a state in which a portion of the base 21 which corresponds to the sixth surface 21 d is gripped, and thus a position of the mirror device 20 in the X-axis direction and the Y-axis direction, and an angle of the mirror device 20 in a plane perpendicular to the Z-axis direction are adjusted based on the plurality of reference holes 13 e formed in the third surface 13 a.

As illustrated in FIG. 3 and FIG. 4 , the fixed mirror 16 is disposed on a side opposite to the mirror device 20 with respect to the optical function member 13, and a position of the mirror device 20 with respect to the base 21 is fixed. For example, the fixed mirror 16 is formed on the fourth surface 13 b of the optical function member 13 by vapor deposition. The fixed mirror 16 includes a mirror surface 16 a perpendicular to the Z-axis direction. In this embodiment, the mirror surface 22 a of the movable mirror 22, and the mirror surface 16 a of the fixed mirror 16 face one side (beam splitter unit 3 side) in the Z-axis direction. The fixed mirror 16 is formed continuously with the fourth surface 13 b of the optical function member 13 to reflect light that is transmitted through the respective light transmitting portions 14 and 15 of the optical function member 13. However, a fixed mirror that reflects light transmitted through the light transmitting portion 14, and a fixed mirror that reflects light transmitted through the light transmitting portion 15 may be provided, respectively.

The stress mitigation substrate 17 is attached to the fourth surface 13 b of the optical function member 13 via the fixed mirror 16. For example, the stress mitigation substrate 17 is attached to the fixed mirror 16, for example, by an adhesive. When viewed from the Z-axis direction, an outer edge of the stress mitigation substrate 17 is located outside of the outer edge 13 c of the optical function member 13. That is, when viewed from the Z-axis direction, the outer edge of the stress mitigation substrate 17 surrounds the outer edge 13 c of the optical function member 13. A thermal expansion coefficient of the stress mitigation substrate 17 is closer to a thermal expansion coefficient of the base 21 of the mirror device 20 (more specifically, a thermal expansion coefficient of the support layer 101) in comparison to a thermal expansion coefficient of the optical function member 13. In addition, the thickness of the stress mitigation substrate 17 is closer to the thickness of the base 21 of the mirror device 20 in comparison to the thickness of the optical function member 13. For example, the stress mitigation substrate 17 is formed in a rectangular plate shape by silicon, and has a size of approximately 16 mm×21 mm×0.65 mm (thickness).

As illustrated in FIG. 1 , the mirror unit 2 configured as described above is attached to the support 9 by fixing a surface of the stress mitigation substrate 17 on a side opposite to the optical function member 13 to a surface 9 a of the support 9 (surface on the one side in the Z-axis direction), for example, by an adhesive. When the mirror unit 2 is attached to the support 9, as illustrated in FIG. 8 , a position of the mirror device 20 in the X-axis direction and the Y-axis direction and an angle of the mirror device 20 in a plane perpendicular to the Z-axis direction are adjusted based on a reference hole 9 b that is formed in the support 9. In FIG. 8 , the second support structure 12 is not illustrated.

[Configuration of First Support Structure and Beam Splitter Unit]

As illustrated in FIG. 1 and FIG. 8 , the first support structure 11 includes a frame body 111, a light transmitting member 112, and a plurality of lead pins 113. The frame body 111 is formed so as to surround the mirror unit 2 when viewed from the Z-axis direction, and is attached to the surface 9 a of the support 9, for example, by an adhesive such as silver solder. For example, the frame body 111 is formed of ceramic, and has a rectangular frame shape. An end surface 111 a of the frame body 111 on a side opposite to the support 9 is located on a side opposite to the support 9 in comparison to the first surface 21 a of the base 21 of the mirror device 20.

The light transmitting member 112 is formed so as to close an opening of the frame body 111, and is attached to the end surface 111 a of the frame body 111, for example, with an adhesive. The light transmitting member 112 is formed of a material having transparency with respect to the measurement light L0 and the laser light L10, and has a rectangular plate shape for example. Here, the end surface 111 a of the frame body 111 is located on a side opposite to the support 9 in comparison to the first surface 21 a of the base 21 of the mirror device 20, and thus the light transmitting member 112 is separated from the mirror device 20. Accordingly, in the optical module 1, when the movable mirror 22 reciprocates in the Z-axis direction, the movable mirror 22 and the drive unit 23 are prevented from coming into contact with the light transmitting member 112. In the optical module 1, the support 9, the frame body 111, and the light transmitting member 112 constitute a package that accommodates the mirror unit 2.

The respective lead pins 113 are provided in the frame body 111 in such a manner that one end 113 a is located inside of the frame body 111, and the other end (not illustrated) is located outside of the frame body 111. The one ends 113 a of the lead pins 113 are electrically connected to the electrode pads 211 and 212 corresponding to the lead pins 113 in the mirror device 20 by wires (not illustrated). In the optical module 1, an electric signal for moving the movable mirror 22 in the Z-axis direction is input to the drive unit 23 through the plurality of lead pins 113. In this embodiment, a stepped surface 111 b that extends in the X-axis direction on both sides of the optical function member 13 in the Y-axis direction is formed in the frame body 111, and one end 113 a of each of the lead pins 113 is disposed on the stepped surface 111 b. The lead pin 113 extends in the Z-axis direction on both sides of the support 9 in the Y-axis direction, and the other end of the lead pin 113 is located on the other side in the Z-axis direction in comparison to the support 9.

As illustrated in FIG. 10 , the beam splitter unit 3 is attached to a surface 112 a of the light transmitting member 112 on a side opposite to the mirror device 20, for example, by an optical adhesive that also functions as a refractive index matching agent. The beam splitter unit 3 includes a first mirror surface 31, a second mirror surface 32, and a plurality of optical surfaces 33 a, 33 b, 33 c, and 33 d. The beam splitter unit 3 is constituted by joining a plurality of optical blocks 34 and 35. The respective optical blocks 34 and 35 are formed of a material having a refractive index that is the same as or similar to that of the optical function member 13. FIG. 10 is a schematic cross-sectional view of the mirror unit 2 and the beam splitter unit 3 illustrated in FIG. 1 , and in FIG. 10 , the mirror device 20 is schematically illustrated, for example, in a state in which dimensions in the Z-axis direction are enlarged in comparison to actual dimensions.

The first mirror surface 31 is a mirror surface (for example, a half mirror surface) that is inclined with respect to the Z-axis direction, and is formed between the optical block 34 and the optical block 35. In this embodiment, the first mirror surface 31 is a surface that is parallel to the Y-axis direction, has an angle of 45° with respect to the Z-axis direction, and is inclined to be spaced away from the light incident unit 4 as it approaches the mirror device 20. The first mirror surface 31 has a function of reflecting a part of the measurement light L0 and allowing the remainder of the measurement light L0 to be transmitted therethrough, and a function of reflecting a part of the laser light L10 and allowing the remainder of the laser light L10 to be transmitted therethrough. For example, the first mirror surface 31 is formed of a dielectric multi-layer film. The first mirror surface 31 overlaps the light passage portion 24 of the mirror device 20, the light transmitting portion 14 of the optical function member 13, and the mirror surface 16 a of the fixed mirror 16 when viewed from the Z-axis direction, and overlaps the light incident unit 4 when viewed form the X-axis direction (refer to FIG. 1 ). That is, the first mirror surface 31 faces the fixed mirror 16 in the Z-axis direction, and faces the light incident unit 4 in the X-axis direction.

The second mirror surface 32 is a mirror surface (for example, a total reflection mirror surface) that is parallel to the first mirror surface 31, and is formed in the optical block 35 to be located on a side opposite to the light incident unit 4 with respect to the first mirror surface 31. The second mirror surface 32 has a function of reflecting the measurement light L0 and a function of reflecting the laser light L10. For example, the second mirror surface 32 is formed of a metal film. The second mirror surface 32 overlaps the mirror surface 22 a of the movable mirror 22 of the mirror device 20 when viewed from the Z-axis direction, and overlaps the first mirror surface 31 when viewed from the X-axis direction. That is, the second mirror surface 32 faces the movable mirror 22 in the Z-axis direction, and faces the first mirror surface 31 in the X-axis direction.

The optical surface 33 a is a surface perpendicular to the Z-axis direction, and is formed in the optical block 35 to be located on a side opposite to the mirror device 20 with respect to the first mirror surface 31. The optical surface 33 b is a surface perpendicular to the Z-axis direction, and is formed in the optical block 35 to be located on the mirror device 20 side with respect to the second mirror surface 32. The optical surface 33 c is a surface perpendicular to the Z-axis direction, and is formed in the optical block 34 to be located on the mirror device 20 side with respect to the first mirror surface 31. The optical surface 33 b and the optical surface 33 c are located on the same plane. The optical surface 33 d is a surface perpendicular to the X-axis direction, and is formed in the optical block 34 to be located on the light incident unit 4 side with respect to the first mirror surface 31. The respective optical surfaces 33 a, 33 b, 33 c, and 33 d have a function of allowing the measurement light L0 to be transmitted therethrough, and a function of allowing the laser light L10 to be transmitted therethrough.

The beam splitter unit 3 configured as described above is attached to the light transmitting member 112 by fixing the optical surface 33 b and the optical surface 33 c which are located on the same plane to the surface 112 a of the light transmitting member 112, for example, by an optical adhesive. When the beam splitter unit 3 is attached to the light transmitting member 112, as illustrated in FIG. 9 , a position of the beam splitter unit 3 in the X-axis direction and the Y-axis direction, and an angle of the beam splitter unit 3 in a plane perpendicular to the Z-axis direction are adjusted based on the reference hole 9 b formed in the support 9. In FIG. 9 , the second support structure 12 is not illustrated.

Here, the optical path of the measurement light L0 and the optical path of the laser light L10 in the mirror unit 2 and the beam splitter unit 3 will be described in detail with reference to FIG. 10 .

As illustrated in FIG. 10 , when the measurement light L0 is incident to the beam splitter unit 3 in the X-axis direction through the optical surface 33 d, a part of the measurement light L0 is transmitted through the first mirror surface 31, is reflected by the second mirror surface 32, and reaches the mirror surface 22 a of the movable mirror 22 through the optical surface 33 b and the light transmitting member 112. The part of the measurement light L0 is reflected by the mirror surface 22 a of the movable mirror 22, and proceeds on the same optical path P1 in an opposite direction, and is reflected by the first mirror surface 31. The remainder of the measurement light L0 is reflected by the first mirror surface 31, and reaches the mirror surface 16 a of the fixed mirror 16 through the optical surface 33 c, the light transmitting member 112, the light passage portion 24 of the mirror device 20, and the light transmitting portion 14 of the optical function member 13. The remainder of the measurement light L0 is reflected by the mirror surface 16 a of the fixed mirror 16, proceeds on the same optical path P2 in an opposite direction, and is transmitted through the first mirror surface 31. The part of the measurement light L0 which is reflected by the first mirror surface 31, and the remainder of the measurement light L0 which is transmitted through the first mirror surface 31 become interference light L1, and the interference light L1 of the measurement light is emitted from the beam splitter unit 3 through the optical surface 33 a along the Z-axis direction.

On the other hand, when the laser light L10 is incident to the beam splitter unit 3 in the Z-axis direction through the optical surface 33 a, a part of the laser light L10 is reflected by the first mirror surface 31 and the second mirror surface 32, and reaches the mirror surface 22 a of the movable mirror 22 through the optical surface 33 b and the light transmitting member 112. The part of the laser light L10 is reflected by the mirror surface 22 a of the movable mirror 22, proceeds on the same optical path P3 in an opposite direction, and is reflected by the first mirror surface 31. The remainder of the laser light L10 is transmitted through the first mirror surface 31, and reaches the mirror surface 16 a of the fixed mirror 16 through the optical surface 33 c, the light transmitting member 112, the light passage portion 24 of the mirror device 20, and the light transmitting portion 14 of the optical function member 13. The remainder of the laser light L10 is reflected by the mirror surface 16 a of the fixed mirror 16, proceeds on the same optical path P4 in an opposite direction, and is transmitted through the first mirror surface 31. The part of the laser light L10 which is reflected by the first mirror surface 31, and the remainder of the laser light L10 which is transmitted through the first mirror surface 31 become interference light L11, and the interference light L11 of the laser light is emitted from the beam splitter unit 3 through the optical surface 33 a along the Z-axis direction.

As described above, the light passage portion 24 of the mirror device 20 constitutes a first portion P2 a of the optical path P2 of the measurement light L0 and a first portion P4 a of the optical path P4 of the laser light L10 in an optical path between the beam splitter unit 3 and the fixed mirror 16. In addition, the light transmitting portion 14 of the optical function member 13 constitutes a second portion P2 b of the optical path P2 of the measurement light L0 and a second portion P4 b of the optical path P4 of the laser light L10 in the optical path between the beam splitter unit 3 and the fixed mirror 16.

The second portion P2 b of the optical path P2 of the measurement light L0 is constituted by the light transmitting portion 14, thus an optical path difference between both the optical paths P1 and P2 is corrected so that a difference between an optical path length (optical path length in consideration of a refractive index of respective media through which the optical path passes) of the optical path P1 of the measurement light L0, and an optical path length of the optical path P2 of the measurement light L0 decreases. Similarly, the second portion P4 b of the optical path P4 of the laser light L10 is constituted by the light transmitting portion 14, thus an optical path difference between both the optical paths P3 and P4 is corrected so that a difference between an optical path length of the optical path P3 of the laser light L10 and an optical path length of the optical path P4 of the laser light L10 decreases. In this embodiment, a refractive index of the light transmitting portion 14 is the same as a refractive index of the respective optical blocks which constitute the beam splitter unit 3, and a distance between the first mirror surface 31 and the second mirror surface 32 in the X-axis direction is the same as the thickness of the light transmitting portion 14 in the Z-axis direction (that is, a distance between the surface 14 a of the light transmitting portion 14 and the fourth surface 13 b of the optical function member 13 in the Z-axis direction).

[Configuration of Second Support Structure, Light incident unit, and the Like]

As illustrated in FIG. 1 , the second support structure 12 includes a connection unit 120. The connection unit 120 includes a main body portion 121, a frame body 122, and a fixing plate 123. The main body portion 121 includes a pair of side wall portions 124 and 125, and a ceiling wall portion 126. The pair of side wall portions 124 and 125 face each other in the X-axis direction. An opening 124 a is formed in the side wall portion 124 on one side in the X-axis direction. The ceiling wall portion 126 faces the support 9 in the Z-axis direction. An opening 126 a is formed in the ceiling wall portion 126. For example, the main body portion 121 is integrally formed of a metal. A plurality of positioning pins 121 a are provided in the main body portion 121. The main body portion 121 is positioned with respect to the support 9 by inserting the positioning pins 121 a into the reference hole 9 b and the hole 9 c which are formed in the support 9, and is attached to the support 9 in this state, for example, by a bolt.

The frame body 122 is disposed on a surface of the side wall portion 124 on a side opposite to the beam splitter unit 3. An opening of the frame body 122 faces the beam splitter unit 3 through the opening 124 a of the side wall portion 124. The light incident unit 4 is disposed in the frame body 122. The fixing plate 123 is a member that fixes the light incident unit 4 disposed in the frame body 122 to the main body portion 121 (details will be described later).

The second support structure 12 further includes a holding unit 130. The holding unit 130 includes a main body portion 131, a frame body 132 and a fixing plate 133. The main body portion 131 is attached to a surface of the ceiling wall portion 126 which is opposite to the support 9. The main body portion 131 is positioned with respect to the main body portion 121 of the connection unit 120 by a plurality of positioning pins 131 a, and is attached to the ceiling wall portion 126 in this state, for example, by a bolt. A concave portion 134 is formed in a surface of the main body portion 131 which is opposite to the support 9. A first light passage hole 135, a second light passage hole 136, and a third light passage hole 137 are formed in a bottom surface of the concave portion 134. The first light passage hole 135 is formed at a position that faces the first mirror surface 31 of the beam splitter unit 3 in the Z-axis direction. The second light passage hole 136 is formed on the other side of the first light passage hole 135 in the X-axis direction (that is, on a side opposite to the light incident unit 4). The third light passage hole 137 is formed on the other side of the second light passage hole 136 in the X-axis direction.

The frame body 132 is disposed on the bottom surface of the concave portion 134. An opening of the frame body 132 faces the third light passage hole 137. The second light source 7 is disposed in the frame body 132. The first light detector 6 is disposed on the bottom surface of the concave portion 134 in a state of facing the first light passage hole 135. The second light detector 8 is disposed on the bottom surface of the concave portion 134 in a state of facing the second light passage hole 136. The fixing plate 133 is a member that fixes the first light detector 6 and the second light detector 8 which are disposed on the bottom surface of the concave portion 134, and the second light source 7 that is disposed in the frame body 132 to the main body portion 131 (details will be described later).

The light incident unit 4 includes a holder 41 and a collimator lens 42. The holder 41 holds the collimator lens 42, and is configured so that an optical fiber (not illustrated) that guides the measurement light L0 can be connected to the holder 41. The collimator lens 42 collimates the measurement light L0 emitted from the optical fiber. When the optical fiber is connected to the holder 41, an optical axis of the optical fiber matches an optical axis of the collimator lens 42.

A flange portion 41 a is provided in the holder 41. The flange portion 41 a is disposed between the frame body 122 and the fixing plate 123. In this state, fixing plate 123 is attached to the side wall portion 124, for example, by a bolt, and the light incident unit 4 disposed in the frame body 122 is fixed to the main body portion 121. In this manner, the light incident unit 4 is disposed on one side of the beam splitter unit 3 in the X-axis direction, and is supported by the second support structure 12. The light incident unit 4 allows measurement light L0 that is incident from the first light source through a measurement target or measurement light L0 that is generated from the measurement target (in this embodiment, the measurement light L0 guided by the optical fiber) to be incident to the beam splitter unit 3.

A filter 54 is attached to the frame body 122. The filter 54 has a function of cutting off the laser light L10. The filter 54 is disposed in the opening 124 a of the side wall portion 124 in a state of being inclined with respect to an optical axis of the light incident unit 4. The filter 54 closes the opening of the frame body 122 when viewed form the X-axis direction. In this manner, the filter 54 is disposed between the light incident unit 4 and the beam splitter unit 3, and is supported by the second support structure 12 in a state of being inclined with respect to an optical axis of the light incident unit 4. In this embodiment, an optical surface of the filter 54 is a surface that is parallel to the Z-axis direction and has an angle of 10° to 20° with respect to the Y-axis direction. The optical axis of the light incident unit 4 is parallel to the X-axis direction.

The first light detector 6 includes a holder 61, a light detection element 62, and a condensing lens 63. The holder 61 holds the light detection element 62 and the condensing lens 63. The light detection element 62 detects the interference light L1 of the measurement light. For example, the light detection element 62 is an InGaAs photodiode. The condensing lens 63 condenses the interference light L1 of the measurement light incident to the light detection element 62 to the light detection element 62. In the holder 61, an optical axis of the light detection element 62 and an optical axis of the condensing lens 63 match each other.

A flange portion 61 a is provided in the holder 61. The flange portion 61 a is disposed between the bottom surface of the concave portion 134 of the main body portion 131, and the fixing plate 133. In this state, the fixing plate 133 is attached to the main body portion 131, for example, by a bolt, and thus the first light detector 6 disposed on the bottom surface of the concave portion 134 is fixed to the main body portion 131. In this manner, the first light detector 6 is disposed on one side of the beam splitter unit 3 in the Z-axis direction, and is supported by the second support structure 12. The first light detector 6 faces the first mirror surface 31 of the beam splitter unit 3 in the Z-axis direction. The first light detector 6 detects the interference light L1 of the measurement light emitted from the beam splitter unit 3.

The second light detector 8 includes a holder 81, a light detection element 82, and a condensing lens 83. The holder 81 holds the light detection element 82 and the condensing lens 83. The light detection element 82 detects the interference light L11 of the laser light. For example, the light detection element 82 is a Si photodiode. The condensing lens 83 condenses the interference light L11 of the laser light incident to the light detection element 82 to the light detection element 82. In the holder 81, an optical axis of the light detection element 82 and an optical axis of the condensing lens 83 match each other.

A flange portion 81 a is provided in the holder 81. The flange portion 81 a is disposed between the bottom surface of the concave portion 134 of the main body portion 131, and the fixing plate 133. In this state, the fixing plate 133 is attached to the main body portion 131, for example, by a bolt, and thus the second light detector 8 disposed on the bottom surface of the concave portion 134 is fixed to the main body portion 131. In this manner, the second light detector 8 is disposed on one side of the beam splitter unit 3 in the Z-axis direction, and is supported by the second support structure 12. The second light detector 8 detects the interference light L11 of the laser light emitted from the beam splitter unit 3.

The second light source 7 includes a holder 71, a light-emitting element 72, and a collimator lens 73. The holder 71 holds the light-emitting element 72 and the collimator lens 73. The light-emitting element 72 emits the laser light L10. For example, the light-emitting element 72 is a semiconductor laser such as a VCSEL. The collimator lens 73 collimates the laser light L10 emitted from the light-emitting element 72. In the holder 71, an optical axis of the light-emitting element 72 and an optical axis of the collimator lens 73 match each other.

A flange portion 71 a is provided in the holder 71. The flange portion 71 a is disposed between the frame body 132 and the fixing plate 133. In this state, the fixing plate 133 is attached to the main body portion 131, for example, by a bolt, and thus the second light source 7 disposed in the frame body 132 is fixed to the main body portion 131. In this manner, the second light source 7 is disposed on one side of the beam splitter unit 3 in the Z-axis direction, and is supported by the second support structure 12. The second light source 7 emits the laser light L10 that is to be incident to the beam splitter unit 3.

As described above, the holding unit 130 holds the first light detector 6, the second light detector 8, and the second light source 7 so that the first light detector (first optical device) 6, the second light detector (second optical device) 8, and the second light source (third optical device) 7 face the same side, and the first light detector 6, the second light detector 8, and the second light source 7 are aligned in this order. In this embodiment, on one side of the beam splitter unit 3 in the Z-axis direction, the holding unit 130 holds the first light detector 6, the second light detector 8, and the second light source 7 so that the first light detector 6, the second light detector 8, and the second light source 7 face the other side in the Z-axis direction (that is, the beam splitter unit 3 side). In addition, the holding unit 130 holds the first light detector 6, the second light detector 8, and the second light source 7 so that the first light detector 6, the second light detector 8, and the second light source 7 are aligned in this order from one side (that is, the light incident unit 4 side) in the X-axis direction.

A configuration in which the first light detector 6 faces an arbitrary side represents that a light-receiving surface of the light detection element 62 faces the arbitrary side (that is, the first light detector 6 is disposed to detect light incident from the arbitrary side). In this case, for example, lead pins of the light detection element 62 extend to a side opposite to the arbitrary side. Similarly, a configuration in which the second light detector 8 faces an arbitrary side represents that a light-receiving surface of the light detection element 82 faces the arbitrary side (that is, the second light detector 8 is disposed to detect light incident from the arbitrary side). In this case, for example, lead pins of the light detection element 82 extend to a side opposite to the arbitrary side. In addition, a configuration in which the second light source 7 faces an arbitrary side represents that a light emission surface of the light-emitting element 72 faces the arbitrary side (that is, the second light source 7 is disposed to emit light to the arbitrary side). In this case, for example, lead pins of the light-emitting element 72 extend to a side opposite to the arbitrary side. In addition, the holding unit 130 is a part of the second support structure 12. Accordingly, even though the holding unit 130 holds an arbitrary configuration, the arbitrary configuration represents that the arbitrary configuration is supported by the second support structure 12.

A first mirror 51, a second mirror 52, and a third mirror 53 are attached to the main body portion 131 of the holding unit 130. The first mirror 51 is held by the holding unit 130 to be located on a side opposite to the first light detector 6 with respect to the first light passage hole 135. The second mirror 52 is held by the holding unit 130 to be located on a side opposite to the second light detector 8 with respect to the second light passage hole 136. The third mirror 53 is held by the holding unit 130 to be located on a side opposite to the second light source 7 with respect to the third light passage hole 137.

The first mirror 51 is a dichroic mirror that has a function of allowing the measurement light L0 to be transmitted therethrough and of reflecting the laser light L10, and is inclined with respect to the optical axis of the first light detector 6. The first mirror 51 is disposed between the beam splitter unit 3 and the first light detector 6. That is, the first mirror 51 is disposed to face the beam splitter unit 3 and the first light detector 6. In this embodiment, an optical surface of the first mirror 51 is a surface that is parallel to the Y-axis direction and has an angle of 45° with respect to the Z-axis direction. The optical axis of the first light detector 6 is parallel to the Z-axis direction.

The second mirror 52 is a mirror (for example, a half mirror) that has a function of reflecting a part of the laser light L10 and allowing the remainder of the laser light L10 to be transmitted therethrough, and is parallel to the first mirror 51. The second mirror 52 is disposed to overlap the first mirror 51 when viewed from the X-axis direction, and to overlap the second light detector 8 when viewed from the Z-axis direction. That is, the second mirror 52 is disposed to face the first mirror 51 and the second light detector 8. In this embodiment, an optical surface of the second mirror 52 is a surface that is parallel to the Y-axis direction, and has an angle of 45° with respect to the Z-axis direction.

The third mirror 53 is a mirror (for example, a total reflection mirror) that has a function of reflecting the laser light L10 and is parallel to the second mirror 52. The third mirror 53 is disposed to overlap the second mirror 52 when viewed from the X-axis direction, and overlap the second light source 7 when viewed from the Z-axis direction. That is, the third mirror 53 is disposed to face the second mirror 52 and the second light source 7. In this embodiment, an optical surface of the third mirror 53 is a surface that is parallel to the Y-axis direction, and has an angle of 45° with respect to the Z-axis direction.

An aperture 55 is attached to the main body portion 131 of the holding unit 130. The aperture 55 is held by the holding unit 130 to be located between the first mirror 51 and the first light detector 6. The aperture 55 is a member in which an opening having a circular shape is formed when viewed from the Z-axis direction, and is disposed in the first light passage hole 135.

Here, description will be given of an optical path between the beam splitter unit 3 and the first light detector 6, and the like. The interference light L1 of the measurement light, which is emitted from the beam splitter unit 3 in the Z-axis direction, is transmitted through the first mirror 51, is incident to the first light detector 6 through the aperture 55, and is detected by the first light detector 6. On the other hand, the laser light L10 emitted from the second light source 7 is reflected by the third mirror 53, is transmitted through the second mirror 52, is reflected by the first mirror 51, and is incident to the beam splitter unit 3 in the Z-axis direction. The interference light L11 of the laser light, which is emitted from the beam splitter unit 3 in the Z-axis direction, is reflected by the first mirror 51 and the second mirror 52, is incident to the second light detector 8, and is detected by the second light detector 8.

In the optical module 1, a length of an optical path between the beam splitter unit 3 and the first light detector 6 is shorter than a length of an optical path between the beam splitter unit 3 and the second light detector 8, and is shorter than a length of an optical path between the beam splitter unit 3 and the second light source 7. The lengths of the optical paths represent physical distances along the optical paths.

Specifically, a distance from an intersection between the optical path and the first mirror surface 31 of the beam splitter unit 3 to a light incident surface of the first light detector 6 is shorter than a distance from the intersection between the optical path and the first mirror surface 31 of the beam splitter unit 3 to a light incident surface of the second light detector 8, and is shorter than a distance from the intersection between the optical path and the first mirror surface 31 of the beam splitter unit 3 to a light emission surface of the second light source 7. A distance from the intersection between the optical path and the first mirror surface 31 of the beam splitter unit 3 to a light incident surface of the condensing lens 63 of the first light detector 6 is shorter than a distance from the intersection between the optical path and the first mirror surface 31 of the beam splitter unit 3 to a light incident surface of the condensing lens 83 of the second light detector 8, and is shorter than a distance from the intersection between the optical path and the first mirror surface 31 of the beam splitter unit 3 to a light emission surface of the collimator lens 73 of the second light source 7. A distance from the optical surface 33 a of the beam splitter unit 3 to the light incident surface of the first light detector 6 is shorter than a distance from the optical surface 33 a of the beam splitter unit 3 to the light incident surface of the second light detector 8, and is shorter than a distance from the optical surface 33 a of the beam splitter unit 3 to the light emission surface of the second light source 7. A distance from the optical surface 33 a of the beam splitter unit 3 to the light incident surface of the condensing lens 63 of the first light detector 6 is shorter than a distance from optical surface 33 a of the beam splitter unit 3 to the light incident surface of the condensing lens 83 of the second light detector 8, and is shorter than a distance from the optical surface 33 a of the beam splitter unit 3 to the light emission surface of the collimator lens 73 of the second light source 7.

In this embodiment, the light incident unit 4 has a configuration in which angle adjustment of the holder 41 with respect to the frame body 122 is possible. In contrast, the first light detector 6 is positioned by the main body portion 131 when the holder 61 is disposed on the bottom surface of the concave portion 134 of the main body portion 131. Accordingly, in a state in which the first light detector 6 is positioned, the angle adjustment of the holder 41 can be carried out so that detection intensity in the first light detector 6 becomes the maximum while the measurement light L0 is incident to the beam splitter unit 3. In addition, in a state in which the angle adjustment is carried out, the light incident unit 4 can be fixed to the frame body 122.

Similarly, the second light source 7 has a configuration in which angle adjustment of the holder 71 with respect to the frame body 132 is possible. In contrast, the second light detector 8 is positioned by the main body portion 131 when the holder 81 is disposed on the bottom surface of the concave portion 134 of the main body portion 131. Accordingly, in a state in which the second light detector 8 is positioned, the angle adjustment of the holder 71 can be carried out so that detection intensity in the second light detector 8 becomes the maximum while emitting the laser light L10. In addition, in a state in which the angle adjustment is carried out, the second light source 7 can be fixed to the frame body 132.

Not only the light incident unit 4 but also the first light detector 6 may have a configuration in which angle adjustment of the holder 61 with respect to the frame body disposed on the bottom surface of the concave portion 134 of the main body portion 131 is possible. Similarly, not only the second light source 7 but also the second light detector 8 may have a configuration in which angle adjustment of the holder 81 with respect to the frame body disposed on the bottom surface of the concave portion 134 of the main body portion 131 is possible.

[Operation and Effect]

In the mirror unit 2, the optical function member 13 is disposed between the mirror device 20 and the fixed mirror 16, and the base 21 of the mirror device 20 is joined to the optical function member 13. Accordingly, the base 21 is stably held in a state in which deformation of the base 21 is suppressed. Accordingly, in the mirror device 20, it is possible to operate the movable mirror 22 with accuracy. In addition, the light transmitting portion 14 that constitutes a part of the optical path between the beam splitter unit 3 and the fixed mirror 16 is provided in the optical function member 13, and the light transmitting portion 14 is set as a portion that corrects an optical path difference that occurs between the optical path between the beam splitter unit 3 and the movable mirror 22 and the optical path between the beam splitter unit 3 and the fixed mirror 16. Accordingly, it is possible to correct an optical path difference between the both optical paths so that a difference between an optical path length of the optical path between the beam splitter unit 3 and the movable mirror 22 (optical path length in consideration of a refractive index of each medium through which the optical path passes), and an optical path length of the optical path between the beam splitter unit 3 and the fixed mirror 16 decreases. As described above, according to the mirror unit 2, it is possible to constitute the high-accuracy interference optical system.

Particularly, in a case where the optical blocks 34 and 35, and the optical function member 13 are formed of the same material, materials through which light is transmitted are the same as each other, and thus it is possible to suppress occurrence of a property (dispersion) that is different in a refractive index different for each wavelength of a material. That is, it is possible to correct the optical path difference between both the optical paths with respect to all wavelength regions as a target. In a case where the optical blocks 34 and 35 and the optical function member 13 are formed of similar materials, it is possible to correct the optical path difference between the both optical paths with respect to a specific wavelength.

In addition, in the mirror unit 2, the second surface 21 b of the base 21 and the third surface 13 a of the optical function member 13 are joined to each other by direct bonding. Accordingly, it is possible to realize strong joining between the base 21 of the mirror device 20 and the optical function member 13.

In addition, in the mirror unit 2, the third surface 13 a (a joining surface with the mirror device 20) of the optical function member 13 extends to face the plurality of electrode pads 211 and 212 provided in the base 21 of the mirror device 20. Accordingly, it is possible to reliably perform joining of a wire with respect to the electrode pads 211 and 212.

In addition, in the mirror unit 2, the fixed mirror 16 is formed on the fourth surface 13 b of the optical function member 13. Accordingly, it is possible to improve position accuracy and angle accuracy of the fixed mirror 16 with respect to the movable mirror 22 of the mirror device 20. In addition, it is possible to further reduce loss of light in comparison to a case where the fixed mirror 16 is separated from the fourth surface 13 b of the optical function member 13.

In addition, in the mirror unit 2, the optical function member 13 further includes the fifth surface 13 d separated from the mirror device 20 at least in a region where the fifth surface 13 d faces the movable mirror 22. Accordingly, for example, even when a reference position in the case of reciprocating (vibrating) the movable mirror 22 along the Z-axis direction is aligned to the third surface 13 a of the optical function member 13, it is possible to reciprocate the movable mirror 22 along the Z-axis direction while preventing the movable mirror 22 from coming into contact with the optical function member 13. Alignment of the reference position in the case of reciprocating the movable mirror 22 along the Z-axis direction to the third surface 13 a of the optical function member 13 is particularly effective for the case of correcting an optical path difference that occurs between an optical path between the beam splitter unit 3 and the movable mirror 22, and an optical path between the beam splitter unit 3 and the fixed mirror 16.

In addition, in the mirror unit 2, the mirror device 20 is constituted by the SOI substrate 100, and the second surface 21 b (joining surface with the optical function member 13) of the base 21 is a surface opposite to the intermediate layer 103 in the device layer 102, and the mirror surface 22 a of the movable mirror 22 is provided on a surface on the intermediate layer 103 side in the device layer 102. In the SOI substrate 100, the device layer 102 is thinner than the support layer 101. Accordingly, for example, it is possible to make the mirror surface 22 a of the movable mirror 22 closer to the optical function member 13 in comparison to a “configuration in which the second surface 21 b (joining surface with the optical function member 13) of the base 21 is a surface opposite to the intermediate layer 103 in the support layer 101, and the mirror surface 22 a of the movable mirror 22 is provided on a surface opposite to the intermediate layer 103 in the device layer 102.” Accordingly, for example, it is possible to align the reference position in the case of reciprocating the movable mirror 22 along the Z-axis direction to the third surface 13 a of the optical function member 13 in an easy manner (in a small operation amount). Accordingly, it is possible to acquire sufficient optical interference signals while suppressing a reciprocation amount of the movable mirror 22 along the Z-axis direction.

In addition, in the mirror unit 2, the fifth surface 13 d of the optical function member 13 extends to the outer edge 13 c of the optical function member 13 when viewed from the Z-axis direction. Accordingly, even in a case where a gas exists in a region between the movable mirror 22 and the fifth surface 13 d of the optical function member 13, the gas is likely to escape from the region, and thus it is possible to suppress an operation of the movable mirror 22 from being hindered by the gas that exists in the region. Accordingly, it is possible to suppress a voltage necessary to reciprocate the movable mirror 22 along the Z-axis direction.

In addition, in the mirror unit 2, the surface 14 a of the light transmitting portion 14 is located on the same plane as the third surface 13 a of the optical function member 13. Accordingly, for example, in the case of aligning the reference position when reciprocating the movable mirror 22 along the Z-axis direction to the third surface 13 a of the optical function member 13, it is possible to correct an optical path difference between the both optical paths so that a difference between the optical path length of the optical path between the beam splitter unit 3 and the movable mirror 22, and the optical path length of the optical path between the beam splitter unit 3 and the fixed mirror 16 decreases.

In addition, in the mirror unit 2, the base 21 further includes a sixth surface 21 d that is separated from the optical function member 13 in a region including at least a part of the outer edge 21 c of the base 21 when viewed from the Z-axis direction. Accordingly, when joining the second surface 21 b of the base 21 and the third surface 13 a of the optical function member 13 to each other, it is possible to perform handling of the mirror device 20 by gripping the region in which the sixth surface 21 d is provided in the base 21. The region in which the sixth surface 21 d is provided in the base 21 is gripped, and thus it is possible to secure the degree of cleanliness of the second surface 21 b (joining surface with the optical function member 13) of the base 21, and as a result, it is possible to realize strong joining between the base 21 and the optical function member 13.

In the case of performing joining between the base 21 of the mirror device 20 and the optical function member 13 in a chip level (one-to-one), it is possible to select the mirror device 20 with a good quality and the optical function member 13 with a good quality, and thus a yield ratio of the mirror unit 2 is improved.

In addition, in the mirror unit 2, the outer edge 13 c of the optical function member 13 is located outside of the outer edge 21 c of the base 21 when viewed from the Z-axis direction. Accordingly, it is possible to realize strong joining between the base 21 of the mirror device 20 and the optical function member 13. In addition, it is possible to protect the outer edge 21 c of the base 21.

In addition, in the mirror unit 2, the stress mitigation substrate 17 is attached to the fourth surface 13 b of the optical function member 13 via the fixed mirror 16. When the mirror unit 2 is provided in an installation target (in this embodiment, the support 9) via the stress mitigation substrate 17, for example, even in a case where the installation target is deformed, it is possible to suppress the deformation from having an effect on the interference optical system.

Modification Example

As illustrated in FIG. 11(a), the beam splitter unit 3 may be an optical block 35 in which a first mirror surface 31, a second mirror surface 32, and a plurality of optical surfaces 33 a and 33 b are formed. In addition, as illustrated in FIG. 11(b), the beam splitter unit 3 may be a combination of an optical plate 36 in which the first mirror surface 31 is formed, and a member 37 in which the second mirror surface 32 is formed. In the beam splitter unit 3 illustrated in FIG. 11(b), the optical plate 36 and the member 37 are separated from each other.

In addition, with regard to the mirror unit 2, as illustrated in FIG. 12 , in the mirror device 20, the second surface 21 b (joining surface with the optical function member 13) of the base 21 may be a surface opposite to the intermediate layer 103 in the support layer 101, and the mirror surface 22 a of the movable mirror 22 may be provided on a surface opposite to the intermediate layer 103 in the device layer 102. In this case, as in the mirror surface 22 a, it is possible to provide the plurality of electrode pads 211 on the surface opposite to the intermediate layer 103 in the device layer 102, and thus it is possible to realize simplification of a process of manufacturing the mirror device 20, and a process of assembling the mirror unit 2. In addition, even in a case where the fifth surface 13 d located on a further fourth surface 13 b side in comparison to the third surface 13 a is not provided in the optical function member 13, when the support layer 101 in a portion corresponding to the movable mirror 22 and the drive unit 23 is made thin, it is possible to prevent the movable mirror 22 and the drive unit 23 from coming into contact with the optical function member 13 when reciprocating the movable mirror 22 along the Z-axis direction.

In addition, in the mirror unit 2, as illustrated in FIG. 13 , FIG. 14 , and FIG. 15 , the movable mirror 22 and the drive unit 23 of the mirror device 20 may be disposed in an air-tight space (for example, an air-tight space in which the degree of vacuum is maintained to be high, or an air-tight space filled with an inert gas such as nitrogen). The mirror unit 2 illustrated in FIG. 13 , FIG. 14 , and FIG. 15 includes the mirror device 20, the optical function member 13, the fixed mirror 16, a frame body 18, and a light transmitting member 19. In the optical function member 13, the third surface 13 a extends in a frame shape to surround the fifth surface 13 d when viewed form the Z-axis direction. The third surface 13 a extending in the frame shape is joined to the second surface 21 b of the base 21 in the mirror device 20. The optical function member 13 and the base 21 are joined to each other by direct bonding. The fixed mirror 16 is formed on the fourth surface 13 b of the optical function member 13.

The frame body 18 is formed to surround the movable mirror 22 and the drive unit 23 of the mirror device 20 when viewed from the Z-axis direction, and is joined to the first surface 21 a of the base 21 in the mirror device 20. For example, the frame body 18 is formed of glass, and, for example, shows a rectangular frame shape. The base 21 and the frame body 18 are joined to each other by direct bonding. The light transmitting member 19 is formed to cover an opening of the frame body 18, and is joined to an end surface opposite to the mirror device 20 in the frame body 18. For example, the light transmitting member 19 is formed of glass, and, for example, shows a rectangular plate shape. The frame body 18 and the light transmitting member 19 are joined to each other by direct bonding. In a surface of the light transmitting member 19 on the mirror device 20 side, a region that is not joined to the frame body 18 (that is, a region inside of the frame body 18 when viewed from the Z-axis direction) is subjected to antireflection coating (AR coating) with respect to light of a sensitivity wavelength of the optical module 1.

In this embodiment, a plurality of electrode pads 211 and one electrode pad 212 are arranged in a line along one portion extending along the X-axis direction and the other portion in the outer edge of the base 21. In respective rows, the one electrode pad 212 is located at the center. A pair of grooves 18 a are formed in the frame body 18 to correspond to the plurality of electrode pads 211 and the one electrode pad 212 in the respective rows. A pair of grooves 19 a are formed in the light transmitting member 19 to correspond to the plurality of electrode pads 211 and the one electrode pad 212 in the respective rows. According to this, it is possible to connect wires to the respective electrode pads 211 and 212 through the grooves 18 a and the grooves 19 a.

In the mirror unit 2 illustrated in FIG. 13 , FIG. 14 , and FIG. 15 , the movable mirror 22 and the drive unit 23 of the mirror device 20 are disposed in an air-tight space, and thus it is possible to maintain the movable mirror 22 and the drive unit 23 in a highly reliable state. In addition, when the air-tight space is maintained in a decompressed state, it is possible to allow the movable mirror 22 and the drive unit 23 to smoothly operate.

The mirror unit 2 illustrated in FIG. 13 , FIG. 14 , and FIG. 15 can be efficiently manufactured as follows. As illustrated in FIG. 16(a), first, a wafer 18W including a plurality of portions each becoming the frame body 18, and a wafer 19W including a plurality of portions each becoming the light transmitting member 19 are prepared, and the wafer 18W and the wafer 19W are joined to each other by direct bonding in such a manner that one piece of the frame body 18 and one piece of the light transmitting member 19 correspond to each other (first process). Here, as the direct bonding, for example, plasma activation bonding, room-temperature bonding, or the like is selected so as to prevent a variation of characteristics of AR coating formed on the wafer 19W.

Next, as illustrated in FIG. 16(b), a wafer 20W including a plurality of portions each becoming the mirror device 20 is prepared, and the wafer 18W (to which the wafer 19W is joined) and the wafer 20W are joined to each other by direct bonding in such a manner that one piece of the frame body 18 and one piece of the mirror device 20 correspond to each other (second process). Here, as the direct bonding, for example, plasma activation bonding, room-temperature bonding, anodic bonding, or the like is selected. When joining the wafer 18W and the wafer 20W to each other, the anodic bonding that uses an attractive force caused by application of a voltage is particularly effective because it is difficult to mechanically apply an external force to the mirror device 20. In the case of selecting the anodic bonding as the direct bonding, a wafer formed of borosilicate glass is selected as the wafer 18W.

Next, as illustrated in FIG. 17(a), a wafer 13W including a plurality of portions each becoming the optical function member 13 is prepared, and the wafer 20W (to which the wafer 18W and the wafer 19W are joined) and the wafer 13W are joined to each other by direct bonding in such a manner that one piece of the mirror device 20 and one piece of the optical function member 13 correspond to each other (third process). Here, as the direct bonding, for example, plasma activation bonding, room-temperature bonding, or the like is selected. A fixed mirror layer 16L including a plurality of portions each becoming the fixed mirror 16 is formed in the wafer 13W in advance.

Next, as illustrated FIG. 17(b), the wafer including a plurality of portions each becoming the mirror unit 2 (that is, a plurality of portions each including one piece of the frame body 18, one piece of the light transmitting member 19, one piece of the mirror device 20, and one piece of the optical function member 13) is cut into a plurality of the mirror units 2.

As described above, the wafer 13W (in which the fixed mirror layer 16L is formed) including the plurality of portions each becoming the optical function member 13, the wafer 20W including the plurality of portions each becoming the mirror device 20, the wafer 18W including the plurality of portions each becoming the frame body 18, and the wafer 19W including the plurality of portions each becoming the light transmitting member 19 are prepared, joining of the wafers is performed in a wafer level (a joining sequence is not limited to the above-described sequence), and the resultant wafer including a plurality of portions each becoming the mirror unit 2 is cut into a plurality of the mirror units 2. Even when the cutting is performed by blade dicing using water, since the movable mirror 22 and the drive unit 23 of the mirror device 20 are disposed in the air-tight space, it is possible to prevent the movable mirror 22 and the drive unit 23 from being broken by water.

The material of the optical function member 13, the frame body 18, and the light transmitting member 19 is not limited to glass, and for example, the material may be silicon. Particularly, the material of the optical function member 13 and the light transmitting member 19 is selected in accordance with the sensitivity wavelength of the optical module 1 so that the material is set to glass, for example, in a case where the sensitivity wavelength of the optical module 1 is a near infrared region, and the material is set to silicon, for example, in a case where the sensitivity wavelength of the optical module 1 is an intermediate infrared region. In a case where the material of the optical function member 13, the frame body 18, and the light transmitting member 19 is glass, a shape of these parts is formed, for example, by blast processing, etching, or the like. In a case where the material of the optical function member 13, the frame body 18, and the light transmitting member 19 is silicon, the shape of these parts is formed, for example, by etching.

In addition, as illustrated in FIG. 18 , the light passage portion 24 of the mirror device 20 may be a notch that is formed in the base 21. In the mirror device 20 illustrated in FIG. 18 , not only the light passage portion 24 but also the light passage portion 25 is a notch that is formed in the base 21. The light passage portion 24 is a notch that extends from a region between the pair of levers 261 in the base 21 to the outer edge 21 c of the base 21. The light passage portion 25 is a notch that extends from a region between the pair of levers 271 in the base 21 to the outer edge 21 c of the base 21. In the mirror device 20 illustrated in FIG. 18 , the first elastic support unit 26 does not include the first link member 262, and the second elastic support unit 27 does not include the first link member 272. In addition, as illustrated in FIG. 19 , the light passage portion 24 may not be provided in the mirror device 20. In the mirror unit 2 illustrated in FIG. 19 , the light transmitting portion 14 is provided in a portion that does not overlap the mirror device 20 in the optical function member 13 when viewed from the Z-axis direction.

In addition, the drive unit 23 of the mirror device 20 may be provided with three or more elastic support units which elastically support the movable mirror 22. In addition, the drive unit 23 is not limited to a configuration in which the drive unit 23 is constituted by an electrostatic actuator, and may be constituted, for example, by a piezoelectric type actuator, an electromagnetic type actuator, or the like.

In addition, the second surface 21 b of the base 21 and the third surface 13 a of the optical function member 13 may be joined to each other by means (for example, an adhesive such as an UV curable resin) other than the direct bonding. In addition, the fixed mirror 16 may be separated from the fourth surface 13 b of the optical function member 13 as long as the fixed mirror 16 is disposed on a side opposite to the mirror device 20 with respect to the optical function member 13.

In addition, in the configurations of the mirror unit 2 and the optical module 1, there is no limitation to the above-described materials and shapes, and various materials and shapes are applicable to the configurations. In addition, the configurations of the embodiment and the modification example are applicable to configurations in another embodiment and another modification example in an arbitrary manner.

REFERENCE SIGNS LIST

1: optical module, 2: mirror unit, 3: beam splitter unit, 13: optical function member, 13 a: third surface, 13 b: fourth surface, 13 c: outer edge, 13 d: fifth surface, 14: light transmitting portion, 14 a: surface, 16: fixed mirror, 17: stress mitigation substrate, 20: mirror device, 21: base, 21 a: first surface, 21 b: second surface, 21 c: outer edge, 21 d: sixth surface, 22: movable mirror, 100: SOI substrate (semiconductor substrate), 101: support layer, 102: device layer, 103: intermediate layer. 

The invention claimed is:
 1. A mirror unit comprising: a mirror device that includes a base including a first surface and a second surface opposite to the first surface, and a movable mirror supported in the base to be movable along a first direction that intersects the first surface; an optical function member including a third surface that faces the second surface, and a fourth surface opposite to the third surface; and a fixed mirror that is disposed on a side opposite to the mirror device with respect to the optical function member, wherein the optical function member is provided with a light transmitting portion that constitutes a part of an optical path between a beam splitter unit and the fixed mirror, wherein the beam splitter unit constitutes an interference optical system in combination with the movable mirror and the fixed mirror, the light transmitting portion is a portion that corrects an optical path difference that occurs between an optical path between the beam splitter unit and the movable mirror, and the optical path between the beam splitter unit and the fixed mirror, and the second surface of the base and the third surface of the optical function member are attached to each other.
 2. The mirror unit according to claim 1, wherein the second surface of the base and the third surface of the optical function member are joined to each other by direct bonding.
 3. The mirror unit according to claim 1, wherein the fixed mirror is formed on the fourth surface of the optical function member.
 4. The mirror unit according to claim 1, wherein the optical function member further includes a fifth surface that is separated from the mirror device at least in a region where the fifth surface faces the movable mirror.
 5. The mirror unit according to claim 4, wherein the mirror device is constituted by a semiconductor substrate, the semiconductor substrate includes a support layer that is a first semiconductor layer, a device layer that is a second semiconductor layer, and an intermediate layer that is an insulating layer disposed between the support layer and the device layer, the second surface of the base is a surface opposite to the intermediate layer in the device layer, and a mirror surface of the movable mirror is provided on a surface on the intermediate layer side in the device layer.
 6. The mirror unit according to claim 4, wherein the fifth surface of the optical function member extends to an outer edge of the optical function member when viewed from the first direction.
 7. The mirror unit according to claim 1, wherein a surface of the light transmitting portion on the mirror device side is located on the same plane as the third surface of the optical function member.
 8. The mirror unit according to claim 1, wherein the base further includes a sixth surface that is separated from the optical function member in a region including at least a part of an outer edge of the base when viewed from the first direction.
 9. The mirror unit according to claim 1, wherein an outer edge of the optical function member is located outside of the outer edge of the base when viewed from the first direction.
 10. The mirror unit according to claim 1, further comprising: a stress mitigation substrate that is attached to the fourth surface of the optical function member with the fixed mirror interposed therebetween.
 11. An optical module comprising: the mirror unit according to claim 1; and a beam splitter unit that constitutes an interference optical system in combination with the movable mirror and the fixed mirror. 